1. Field of the Invention
The present invention generally relates to heat lamps. More specifically, the present invention relates to heat lamps for improving the temperature uniformity in a field heated by one or more LED heat lamps.
2. Related Art
Chemical vapor deposition (CVD) is a very well known process in the semiconductor industry for forming thin films of materials on substrates, such as silicon wafers. In a CVD process, gaseous molecules of the material to be deposited are supplied to wafers to form a thin film of that material on the wafers by chemical reaction. Such formed thin films may be polycrystalline, amorphous or epitaxial. Typically, CVD processes are conducted at the elevated temperatures to accelerate the chemical reaction and to produce high quality films. Some processes, such as epitaxial silicon deposition, are conducted at extremely high temperatures (>900° C.).
To achieve the desired high temperatures, substrates can be heated using resistance heating, induction heating or radiant heating. Among these heating techniques, radiant heating is the most efficient technique and, hence, is the currently favored method for certain types of CVD. Radiant heating involves positioning infrared lamps around a reaction chamber positioned within high-temperature ovens, called reactors. Unfortunately, radiant energy has a tendency to create nonuniform temperature distributions, including “hot spots,” due to the use of localized radiant energy sources and consequent focusing and interference effects.
During a CVD process, one or more substrates are placed on a wafer support (i.e., susceptor) inside a chamber defined within the reactor (i.e., the reaction chamber). Both the wafer and the support are heated to a desired temperature. In a typical wafer treatment step, reactant gases are passed over the heated wafer, causing chemical vapor deposition (CVD) of a thin layer of the desired material on the wafer. If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. This is also sometimes called a monocrystalline layer because it has only one crystal structure. Through subsequent processes, these layers are made into integrated circuits, producing from tens to thousands or even millions of integrated devices, depending on the size of the wafer and the complexity of the circuits.
Various process parameters must be carefully controlled to ensure a high quality of layers resulting from CVD. One such critical parameter is the temperature of the wafer during each treatment step of wafer processing. During CVD, for example, the wafer temperature dictates the rate of material deposition on the wafer because the deposition gases react at particular temperatures and deposit on the wafer. If the temperature varies across the surface of the wafer, uneven deposition of the film occurs and the physical properties will not be uniform over the wafer. Furthermore, in epitaxial deposition, even slight temperature non-uniformity can result in crystallographic slip.
In the semiconductor industry, it is important that the material be deposited uniformly thick with uniform properties over the wafer. For instance, in Very Large and Ultra Large Scale Integrated Circuit (VLSI and ULSI) technologies, the wafer is divided into individual chips having integrated circuits thereon. If a CVD process step produces deposited layers with nonuniformities, devices at different areas on the chips may have inconsistent operation characteristics or may fail altogether.